Motor vehicles are typically equipped with a variety of sensors, some of which are used to activate systems which protect vehicle occupants. These systems are known as passive restraint systems, and include front and side airbags, seatbelt pretensioners, and the like.
Recently investigation has begun on systems which protect pedestrians involved in a vehicle collision. For example, US Patent Application Publication No. 2004/0066286 A1 discloses a system for sensing whether an object, which struck a vehicle, is a pedestrian. If it is determined that a vehicle has struck a pedestrian, the system activates a collision protection apparatus such as an external inflatable member to protect the pedestrian from impacting the vehicle hood, and shifting the hood into a raised position that permits it to absorb forces applied by the pedestrian impact. Whether to deploy the collision protection apparatus depends upon the location and length of the impact to the vehicle.
Another technique for detecting object impact is using a piezoelectric cable sensor. Using this technique, the magnitude of a signal from the piezoelectric cable sensor is compared to a threshold value. If the magnitude is greater than a threshold value, it is determined that a particular type of object has impacted on the sensor. However, due to the overlap in signals between different types of objects, the piezoelectric cable sensor technique is not able to accurately distinguish between different types of objects.
There are two critical components to the aforementioned pedestrian impact protection systems—speed and accuracy of the impact detection. With regard to the speed component, if a decision to deploy a pedestrian impact protection system is not timely, it may not deploy fast enough to provide the desired protection for the pedestrian. Furthermore, due to the costs involved with replacing airbags or resetting other types of pedestrian impact protection systems, it is desirable that these systems are only deployed when there is an actual pedestrian impact. Accordingly, it would be desirable to provide systems and methods for quickly and accurately detecting pedestrian impacts.